A balanced diet has to include 5 groups of food substances - carbohydrates, lipids, proteins, minerals and vitamins - but also water and ﻿fibre﻿. They also should be taken in the right amounts to stay healthy.

Carbohydrates

Carbohydrates make up around 5% of the mass of the human body, and are very important. In fact, they are the main 'fuel' that gives us energy. The carbohydrates provide us with glucose (C6H12O6) and sugars, which is what gives us the energy. We get most of our carbohydrates from starch (see diagram below). This is a large, insoluble molecule that can be found in foods like rice, potatoes, wheat and millet.

Sugars

Different foods contain different sugars. For example, fruit sugar is called fructose, milk sugar called is lactose and ordinary table sugar is called sucrose. Sugars have two distinct properties: they are all soluble in water and they all taste sweet. We can get many of our needed sugars from natural foods like fruits and vegetables. However, too much sugar has problems as well. It can cause tooth decay as bacteria feed on sugar from the mouth, breaking it down and making acids that dissolve the tooth enamel. Once it gets through the enamel, it breaks down softer layers beneath, and eventually a cavity is formed.

The diagram on the left shows the structure of glucose and fructose as molecules on their own. If one of each is bonded together, it forms sucrose. A chain of glucose creates a polymer called starch. Another polymer of glucose (in other words, when glucose is in a large chain (like in starch)) is cellulose.

Lipids (fats and oils)

Lipids, like glucose and other carbohydrates, contain the same three elements (carbon, hydrogen and oxygen) but their is much less oxygen in lipids. An example of a fat is tristearin, which is found in beef and lamb. Tristearin has the formula C51H98O6.

Lipids make up 10% of our body's mass. They have many important uses. For example, they from part of the structure of your cells and are used as long term stores of energy. There is a layer under the skin that acts as insulation. There are fats around organs as well that prevent them from external damage.

Chemically, lipids are made of two main types of molecule, namely glycerol and fatty acids. Glycerol is an oily liquid. In a lipid, glycerol is joined to three fatty acids. There are many different fatty acids. Too much lipid is unhealthy, especially saturated fat and cholesterol. These can cause heart disease.

Proteins

Proteins make up around 18% of the mass of the human body. All cells contain protein, so it is a vital substance for growth and repair of tissues. Meat, fish and cheese are especially rich in protein. Despite how important it is, we do not need a lot of it to stay healthy. Doctors recommend a daily amount of 70g.

Protein is a bit like starch in the way that it is a polymer of one element (glucose). However, protein does not have just one element as a building block. Instead, it has 20 different sub-units, called amino acids. All amino acids contain four different elements: carbon, hydrogen, oxygen and nitrogen. Two amino acids also contain sulfur. Different types of proteins have different functions, for example, collagen and keratin are structural proteins in the skin and nails and hemoglobin is a protein in red blood cells. Enzymes also count as proteins.

Minerals

Minerals are present all around the body and carry out vital roles:

Calcium - used to make teeth and bones. It is found in dairy products, fish, vegetables and bread.Iron - It is in the blood. Without the iron, our blood would not be able to carry oxygen as it is a part of the hemoglobin. It is found in red meat, liver, eggs and some vegetables.Phosphorus - used to make teeth and bones, and is part of our DNA. It is found in most foods.Sodium and Chlorine - It is found in the blood and other body fluids. It is found in common salts and in most other foods.Magnesium - Used to make bones. It is found inside cells. Many green vegetables contain it.

If people do not get enough minerals, they can get a mineral deficiency disease. For example, a lack of calcium can result in poor bone development and even rickets, or if there is a lack of iron it can result in anaemia. This means that they get tired and lack energy since the blood does not carry enough oxygen.

Vitamins

Different vitamins function differently and are needed in the correct amounts to stay healthy.

Vitamin A - Needed to make a chemical in the retina of the eye. A lack of it causes night blindness, which makes it difficult to see in dim lightVitamin D - Needed to grow bones. A lack of it can cause rickets, just like with calcium.Vitamin C - Needed to make a fibre that connects cells and bonds them together. A lack of it can cause scurvy, where wounds do not heal and there is excessive bleeding.Vitamin B - Vitamin B is a collection of different substances, namely thiamine, riboflavin and niacin. These help with cell respiration. A lack of this vitamin causes weakened muscles and paralysis.

We need a small amount of vitamins in our diet, but they are essential to stay healthy.

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